This is a step-by-step work-in-progress guide to help you build your own scenarios in unity of command 2.
I am playing the game in german, so there may be a few translation issues.
Also english is not my first language, so please excuse any errors.

By now you can only create single-player scenarios in the scenario editor.

When creating the scenario you have 5 input fields:

- scenarioname (the name of the folder that will be created)
- UV (the area on the map where your scenario will take place; its made of an x and y coordinate; you can change this later on)
Example Points on the europe map:

• Top left corner - 0,0 (atlantic ocean)
  
• London - 136,160
  
• Paris - 143,182
  
• Berlin - 209,165
  
• Rome - 193,243
  
• Munich - 194,197
  
• Vienna - 222,199
  
• Warsaw - 248,169
  
• Koenigsberg - 246,151
  
• Marseilles - 150,227
  
• Bordeaux - 116,208

- faction 1 and 2: faction 1 will be the one controlled by the player

• Available factions: allies, axis, soviet, neutral(finnish)

- map: there are currently 3 maps:

• louisiana (75,64) - small map used in the tutorial of the game
  
• normandy_2 (56,48) - small map of the normandy in a larger map-scale
  
• europe_10 (503,368) - map of europe, not all parts are completely designed, the most detailed
  parts are the one used for the "Victory in the West"-campaign

Useful Shortcuts:
CTRL + S : Saving the scenario
CTRL + Q : Closing the scenario editor
U : Zooming in
I : Zooming out
H : Show Grid
F : Toggle Fog of War
Z : Show coordinates of each hex
V : Show player supply
B : Show enemy supply

In the scenario properties you can now set some basic things about your scenario.

There is an Guide from the Steam user J-manByte on how you can set the playable area in the editor:
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=1971010989

Now you should set the hex ownership for each tile. (Shortcut : "3")
Hex ownership determines whish faction controls this territory.
Land units can only be placed on tiles where the ownership is set for the corresponding side.
You can swap the selected faction ownership with Space and change a hex by clicking on it.

With "4" you can create missiongoals.
With "5" you can create supply sources.
By selecting each one of these and hitting enter you can edit their properties.
Creating a supply source on a railroad or road automatically expands the supply network for this faction.
Supply sources are usually located on the edge of the playable area or in city centres.

With "6" you can create supply points.
These points need to be on a railroad or road that is connected to a supply source to be effective. Otherwise they are marked red.
You can expand their range by clicking multiple times on one hex and decrease their range or delete them by shift-clicking.

With "7" you can create Battleships.
With "8" you can create Landing Craft(LCVP).
These can obviously only be placed on water.
In the properties window of the battleships you can set the turn they arrive and the number of turns they shall stay. In the last textfield you can set the tiles that they will be able to fire upon.
Example:

With "9" you can create Parachute planes.
With "0" you can place stragglers. You can remove them by shift-clicking.

WIth "Space" you can destroy/repair bridges by clicking on them.

In the menu on the right you can also edit the strategic support.

After this setup we can now create some units. To do this you first need to create at least one HQ for each side.
Click on campaign properties in the top right corner. In the bottom left corner you can set a name for the HQ select its nationality and then add it.

Now you can create units with the input fields above.
You can find a full list of unit types available at

...\steamapps\common\Unity of Command 2\_packages\base\data\entity_types\unit_types

After you created the HQ's and units you can place them with "1" - units, "2" -HQ's.
By selecting units or HQ's and hitting enter you can edit their properties.
When you have selected a unit you can vary their step-count with the mouse wheel.

These are the first steps required to create your own scenario.
When you are done with editing you should test your scenario to check for mistakes and to make balance adjustments.
After that you can upload your scenario to the steam workshop at the bottom of the scenario properties window.

Feel free to comment if you have anything to add or if you catch any mistakes done by me.
You can also ask questions and i will try to answer them as soon as possible.
I will continue to complement this text and add more details if needed.

At

%LocalAppData%/.uoc2/_packages/campaign_name/data/scenarios/campaign_name.usc/scenarios/scenario_name

is a folder for your scenario.

You can configure almost everything in your scenario by editing the .yml-files in this folder.
But you need to be careful what you modify here or your scenario will not be playable anymore.